The effects of inhibitors of poly-(ADP-R) synthesis on x-ray break resealing were examined using alkaline elution. These compounds slowed but did not prevent DNA strand break ligation in L1210 cells. Further, this effect was reproduced in human fibroblasts including cells from patients with ataxia telangiectasia (A-T) which are putatively deficient in polymer synthesis following x-ray. Direct examination of poly-(ADP-R) synthesis in normal and A-T fibroblasts revealed no differences in our studies. This slowing of x-ray break resealing was also demonstrated using the nucleoid sedimentation technique. Additionally, this technique allowed the description of a second phase to x-ray DNA damage repair which most probably corresponds to reconstitution of the normal supercoiled structure of chromatin.